Why putchar() and getchar() are accepting more than one character when using while loop..?

Question

Here, I have understood why putchar() is printing only the first character that is 'C'

#include <stdio.h>
main(){
    int c;
    c = getchar();
    putchar(c);
}

output : > Cprograming
         > C

But, When using a while loop the behavior of those functions is changing.

#include <stdio.h>
main(){
    int c;
    c = getchar();
    while(c != 2){
        putchar(c);
        c = getchar();
    }
}

output : > Cprograming
         > Cprograming
         > Bells and Wistles
         > Bells and Wistles
         ...

Why suddenly getchar() and putchar() are storing and printing more than one character..?? Why is this happening..??

I tried to practice it this way.

int c,d,e,f,g;
    c = getchar();
    putchar(c);
    d = getchar();
    putchar(d);
    e = getchar();
    putchar(e);
    f = getchar();
    putchar(f);
    g = getchar();
    putchar(g);

This is my assumption how program might be working.

Start with c = getchar()

User enter 'Qwerty'

getchar() stores this 'Qwerty' one by one character in something called input buffer(sorry for technical words)

user hits enter, getchar() returns the first character from buffer and store it into c

putchar(c), sends this value to something called output buffer, Now output buffer has Q stored in it . Next, d = getchar(), now this new getchar(), goes to the input buffer asks for the top character stored in it and return it to 'd'

putchar(d), sends this new d value to output buffer, and now output buffer contains 'Qw'

--this repeats until we don't have enough getchar() & putchar() or we run out of characters.

In this case, we don't have enough getchar() & putchar(). So, the output screen will look something like this

Qwerty
Qwert

My question is,

Why d = getchar(); collects character from buffer. Why it does not just start a new stream for itself...?

I mean c = getchar(); says ok start typing
and

d = getchar(); No, don't start typing. first check if buffer has something left. if it doesn't only then start typing.

Why..?

I'm really sorry if I'm being absolutely silly. Just a beginner programmer. Hope you guys understand.

Answer 1

Getchar will take the input in a stream and when he does it he does not delete the stream.

The thing is he get a data then you print you check the while then you go in getchar then you read the next data in the stream

try it by yourself with this

#include <stdio.h>
int main(){
    int c;
    c = getchar();
    while(c <= 50){
        putchar(c);
        c = getchar();
    }
    return 0;
}

and use random number you will see it will stop when he find a number with an ascii value more or equal to 51

Answer 2

The while loop, re-executes the statements as long as the validation condition remains true. Delayed echo output illustrates buffered input, when the entered characters are accumulated and stored in a time domain called a buffer. Pressing a key -Enter- makes the block of typed characters available to the program.